An ion trap time-of-flight mass spectrometer (IT-TOFMS) has been known as a type of mass spectrometer. In an IT-TOFMS, ions generated in an ion source are temporarily stored in an ion trap, and an ion selection is performed so that only ions having a specific mass (to be exact, a mass to charge ratio m/z) are left in the ion trap. After that, a collision-induced dissociation gas is introduced into the ion trap and the remaining ions are dissociated as precursor ions. A variety of product ions generated by the dissociation are collectively ejected from the ion trap to be introduced into the TOFMS, where they are mass-analyzed. That is, by performing an MS/MS analysis, it is possible to obtain mass spectra of a variety of product ions generated by the dissociation of precursor ions originating from the sample.
As an ion trap, a three-dimensional quadrupole ion trap, a linear ion trap, and other types of ion traps are known. In general, however, the mass selectivity (mass resolving power) of ions in such an ion trap is not always high. Hence, if there is an ion or ions which have a mass that is very close to that of the target precursor ion, it is difficult to exclude such ions from the process of dissociateing the target precursor ion.
In recent years, the importance of accurately identifying a macromolecule such as protein has been increasing. However, with an MS/MS analysis in which an ion trap and a TOFMS are combined as previously described, it is difficult to obtain accurate structure information on a target component. Given this factor, in order to particularly enhance the mass selectivity of a precursor ion, a MALDI-TOF/TOF mass spectrometer has been recently known in which various kinds of TOF mass analyzers, such as a liner TOF, a reflection TOF, and a helical orbit TOF, are combined in two stages (refer to Patent Document 1 and other documents). However, with such a conventional TOF/TOF mass spectrometer, for one ejection of ions from an ion source, only one kind of ions included in the ejected ions can be MS/MS analyzed. Therefore, when it is required to obtain the structure information on a plurality of components contained in the sample, an ionization process and an MS/MS analysis must be repeated, which makes it difficult to enhance the throughput of the analysis.
[Patent Document 1] JP-A 2007-333528
[Patent Document 2] JP-B 4033133